A jet engine for an aircraft is constituted by the successive arrangement of a fan that takes in air, a compressor that takes in and compresses a portion of the air that the fan has taken in, a combustor that mixes the air that the compressor has compressed and fuel and causes a combustion, and a turbine that drives the fan and the compressor with the combustion gas of the combustor.
The compressor, the combustor and the turbine are allocated in a cylindrical partition wall, and the fan is allocated in the upstream of the cylindrical partition wall. A large portion of the air that the fan takes in passes along a bypass duct that is provided in a space which exists between the cylindrical partition wall and a casing that covers the outer periphery of the cylindrical partition wall. The air that passes through this bypass duct (bypass stream) is discharged so as to surround the outer circumference of the exhaust air of the turbine (core stream), and merges with the core stream.
The region where this core stream and bypass stream merge serves as a noise generation source, leading to the generation of noise. In order to reduce this noise, it has been proposed to have a plurality of pyramidal bodies arranged on a downstream end portion of a cylindrical partition wall to guide a portion of the high-speed core stream and the low-speed bypass stream in mutually different directions, and efficiently mix the fluids that flow on the inner side and the outer side of the cylindrical partition wall (for example, refer to Patent Document 1 and Non-Patent Document). Thereby, the core stream and the bypass stream are suitably mixed by the generation of a vortex, and it is possible to reduce the noise.
However, since the pyramidal bodies are permanently fixed to the cylindrical partition wall, the core stream and the bypass stream end up being mixed not only at the time of takeoff but during cruising as well, and thus more than needed, leading to the problem of a reduction in thrust during cruising. Therefore, it has been proposed to arrange nozzles on the cylindrical partition wall, and by suitably injecting air toward the merging portion of the core stream and the bypass stream, the mixture state is adjusted (for example, refer to Non-Patent Document 2).
Jet engines are mounted to airplane wings via a pylon.
In the downstream region of this pylon, as shown in FIG. 6, the core stream X is deflected by turbulence in the bypass stream Y so that a low-speed ambient air stream Z that is further outside the core stream X and the bypass stream Y approaches. At this time, since the speed differential between the core stream X and the ambient air stream Z is large, a high shearing stress region with rapid fluctuations in speed is produced in the boundary region, and thus serves as another noise generation source in addition to the aforementioned noise generation source.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-172205
[Non-Patent Document 1] Steven J. Massey et al., “Computational Analyses of Propulsion Aeroacoustics for Mixed Flow Nozzle Pylon Installation at Takeoff”, NASA/CR-2001-211-56, September 2001.
[Non-Patent Document 2] Brenton Greska et al., “The Effects of Microjet Injection on an F404 Jet Engine”, AIAA 2005-3047, 11th AIAA/CEAS Aeroacoustics Conference (26th AIAA Aeroacoustics Conference), 23-25 May 2005.
Accordingly, in the nozzles disclosed in Non-Patent Document 2 above, it is not possible to reduce the noise from the aforementioned new noise generation source, and the noise reduction effect is insufficient.
The present invention was achieved in view of the above circumstances, and has as its object to provide a noise reducing device for a jet engine and a jet propulsion system that can reduce the noise that is produced as a result of the jet engine being connected to the wing of an airplane by a pylon.